1. Field of the Invention
This invention relates to a linkage assembly for transmitting forces along a single axis and especially to such a linkage assembly which can also move in any direction in a plane normal to its axis.
The inventor has filed a copending U.S. patent application for a "Shear Motor for Dynamic Mount for Laser-Beam Mirror" Ser. No. 610,461, filed May 15, 1984, now U.S. Pat. No. 4,775,815, incorporated herein by reference.
2. Description of the Prior Art
High-energy laser (HEL) systems generally employ an adjustable, cooled mirror to steer the laser beam. The mirrors are large and heavy, and beam control requires precise pointing, focusing and stabilization of the beam in a severely vibrational environment. To date, a mirror mounting-and-moving device capable of satisfactorily performing these control functions has not been demonstrated even though extensive effort has been expended thereon.
Perturbations arising from acoustic, thermal and maneuvering loads in the mirror, its mount and its dynamic actuator require the actuator (or motor) to be capable of providing several milliradians of stroke and to have an operating bandwidth from D.C. to several kilohertz (KHz). Stroke precision is on the order of a few microradians. The high intensity of the beam on the mirror surface and the low allowable distortion of the mirror surface combine with high dynamic loads to increase mirror size and weight (in excess of 30 lbs.).
In an operating system, the dynamic mirror mount actuators are driven by a "closed loop", electronic servo system. Error signals may be obtained from a variety of optical sensor arrangements depending upon specific system considerations. In all cases, however, stability of a practical servo drive requires that structural resonances of the actuator drive train be higher than operating frequencies. Control of heavy heat exchanger-type mirrors (cooled mirrors) at several kilohertz requires actuator spring rates of tens of millions of pounds per inch of deflection.
Conventional piezoceramic actuators require excessive length to achieve required deflections, the resultant structural proportions resulting in excessively low resonance characteristics. Practical power considerations preclude high-frequency operation at high voltage. The unique piezoceramic shear motor used in the present dynamic mirror mount provides a displacement per volt which is six times as much as that provided by a conventional PZT actuator. The block-like proportions are ideally suited to high structural resonance design. Also, the configuration used is inherently reactionless.
The dynamic mirror mount also requires a stiff linkage to transfer actutor movements into mirror movements. The linkage must not only be stiff, it must be completely flexible in a plane orthogonal to the axis along which the actuator movements are transmitted to adjust for non-axially directed actuator forces.